1. Field of the Invention
The present invention relates to a novel cross-copolymerized olefin/aromatic vinyl compound/diene copolymer (hereinafter sometimes abbreviated as a cross-copolymer) and its composition, and further processes for their production.
2. Discussion of Background
Ethylene/aromatic Vinyl Compound (styrene) Copolymers
Some ethylene/aromatic vinyl compound (styrene) random copolymers obtainable by means of a so-called uniform type Ziegler-Natta catalyst system comprising a transition metal catalyst component and an organic aluminum compound, and processes for their production, are known.
JP-A-3-163088 and JP-A-7-53618 disclose ethylene/styrene copolymers having a styrene content of at most 50 mol % and containing no normal (i.e. head-to-tail) styrene chain, so-called pseudo-random copolymers, obtainable by means of a complex having a so-called constrained geometric structure.
JP-A-6-49132 and Polymer Preprints, Japan, 42, 2292 (1993) disclose processes for producing similar ethylene/styrene copolymers having an aromatic vinyl compound content of at most 50 mol % and containing no normal aromatic vinyl compound chain, i.e. pseudo-random copolymers, by means of a catalyst comprising a crosslinked metallocene type Zr complex and a cocatalyst. These copolymers have no stereoregularity derived from aromatic vinyl compound units.
Further, recently, it has been reported to produce an ethylene/aromatic vinyl, compound copolymer having a stereoregularity of alternating copolymerization type by means of a certain specific crosslinked bisindenyl type Zr complex i.e. a racemic[ethylenebis(indenyl)zirconium dichloride] under an extremely low temperature (−25° C.) condition. (Macromol. Chem., Rapid Commun., 17, 745 (1996).) However, with the copolymer obtainable by this complex, the molecular weight is not yet practically sufficient, and the compositional distribution is also large.
Further, JP-A-9-309925 and JP-A-11-130808 disclose novel ethylene/styrene copolymers which respectively have styrene contents of from 1 to 55 mol % and from 1 to 99 mol % and which have ethylene/styrene alternating structures and isotactic stereoregularity in their styrene chain structures and further have head-to-tail styrene chain structures, with the alternating degrees (λ values in this specification) of the copolymers being at most 70. Further, these copolymers have high transparency.
The physical properties of various ethylene/styrene random copolymers mentioned above, are strongly influenced by the compositions (the styrene contents) when their molecular weights are sufficiently high. Namely, a copolymer having a relatively low styrene content at a level of at most 20 mol %, has crystallizability based on the polyethylene chains, whereby it may have heat resistance at a level of from 80° C. to 120° C. and further has high mechanical properties. However, if the styrene content becomes higher, the crystallizability derived form the polyethylene chains tends to decrease or diminish, and the heat resistance and mechanical properties tend to decrease. When there is stereoregularity in ethylene/styrene alternating structures, and relatively many such alternating structures are contained, the crystallizability derived from such alternating structures will appear, but there may sometimes be a problem with respect to the crystallinity or the crystallization rate. In a copolymer having a high styrene content of at least 60 mol %, many isotactic styrene chain structures are contained, but isotactic styrene chains have a low crystallization rate, whereby it may lack in practical applicability as a heat resistant resin.
On the other hand, a copolymer having a low styrene content is excellent also in cold resistance (embrittle temperature) at a level of −60° C. However, as the styrene content increases, the cold resistance tends, to deteriorate, and in the vicinity of 30 mol %, it will be about −10° C., and in the vicinity of 50 mol %, it will be about room temperature.
A copolymer having a styrene content of from about 15 to 50 mol %, has a feeling, flexibility and stress relaxation property similar to polyvinyl chlorides and is useful as a substitute for polyvinyl chlorides. Further, it is excellent in vibration-damping properties and soundproofing properties. However, its heat resistance and cold resistance are poor, whereby it is hardly useful by itself.
When used as a stretch film, a copolymer having a styrene content of from about 30 to 50 mol % shows slow elongation recovery properties similar to a polyvinyl chloride stretch film at room temperature, but it tends to be too stiff under a refrigerating or freezing condition. Further, when it is attempted to produce this film by inflation molding or extrusion molding with a T-die, the film itself has a high self-tack property, and during winding, the film tends to adhere to itself. A self-tack property to some extent is effective for a substitute for a polyvinyl chloride film, especially as a stretch film for food packaging, but it can hardly be compatible with film moldability.
An ethylene/styrene copolymer having a styrene content of at least 40 mol % is excellent in printability and tinting property and has an improved compatibility with a styrene type resin. Especially, a copolymer having a styrene content of at most 20 mol % is inferior in printability and tinting property, but is excellent in compatibility with a polyolefin type resin.
These random ethylene/styrene copolymers show remarkable changes in the physical properties and compatibility depending upon the compositions as described above, and they have had a problem that with a single composition, various properties (such as heat resistance, cold resistance and stress relaxation property or flexibility) can not be satisfied at the same time.
In order to solve such a problem, it has been proposed to mix ethylene/styrene copolymers having different compositions to obtain a composition (JP-A-2000-129043, WO98/10018), to mix them with polyolefins to obtain compositions (WO98/10015), or to crosslink them (U.S. Pat. No. 5,869,591). However, ethylene/styrene copolymers substantially different in their compositions have poor compatibility to one another, and their compositions or compositions with polyolefins tend to be opaque, and the mechanical properties may sometimes be impaired, whereby the application may be limited. Further, in the case of crosslinking, there is a problem that the secondary moldability or recycling property tends to be lost, or the production cost tends to increase.
Ethylene/α-olefin Copolymers
Ethylene/α-olefin copolymers, in which 1-hexene, 1-octene or the like is co-polymerized to ethylene, i.e. so-called LLDPE, are flexible and transparent and have high strength, whereby they are widely used as e.g. films for general use, packaging materials or containers. However, as a nature of polyolefin type resins, their printability and coating properties are low, and special treatment such as corona treatment will be required for printing or coating. Further, they have poor affinity with an aromatic vinyl compound polymer such as a polystyrene or a polar polymer, and in order to obtain a composition with such a resin having good mechanical properties, it has been necessary to employ an expensive compatibilizing agent additionally.
Common Graft Copolymers
As a method for obtaining a graft copolymer, a method has been heretofore known wherein a graft copolymer of an olefin type polymer or an olefin/styrene type copolymer is obtained during the polymerization or during the mold processing by a common known radical graft treatment. However, by this method, it has been difficult to obtain high graft efficiency, and the method is disadvantageous from the viewpoint of costs. Further, the obtainable graft copolymer usually has a problem that it is non-uniform and partially gelled to be not melting, whereby the moldability tends to be impaired. The graft copolymer thus obtained, usually has graft chains independently branched from the polymer main chain, but when such copolymer is employed as a composition or a compatibilizing agent, the strength of the interface of the polymer microstructure can not be said to be sufficient.